YARA 4.5.0 was released with a small change to the regex syntax (allowing more whitespace) and many bugfixes.

Victor considers that although YARA-X (the rewrite of YARA in Rust) is still in beta, you can start to use it now.

From his blog post "YARA is dead, long live YARA-X":

YARA-X is still in beta, but is mature and stable enough for use, specially from the command-line interface or one-shot Python scripts. While the APIs may still undergo minor changes, the foundational aspects are already established.

Didier Stevens
Senior handler
blog.DidierStevens.com